Conventional cruise control systems regulate the speed of a vehicle at a pre-determined value. Basically, conventional cruise control systems control the speed of a vehicle by actuating the vehicle""s throttle. Adaptive cruise control (xe2x80x9cACCxe2x80x9d) systems provide enhancements to conventional cruise control systems. Generally, ACC systems control the speed of a vehicle (the xe2x80x9cACC vehiclexe2x80x9d) based on the identification of vehicles preceding the ACC vehicle (xe2x80x9cpreceding vehiclesxe2x80x9d) that are in the path of or in the same lane as the ACC vehicle (xe2x80x9ctarget vehiclesxe2x80x9d). A preceding vehicle is considered to be xe2x80x9cin the pathxe2x80x9d of an ACC vehicle if the positional relationship between the preceding and ACC vehicles is such that if the ACC vehicle remains on its course and travels faster than the preceding vehicle, it will eventually collide with the preceding vehicle. ACC systems control the ACC vehicle""s speed to follow a value set by the ACC vehicle operator when no target vehicles have been identified. However, when the target vehicle has been identified and is moving more slowly than the ACC vehicle, the ACC system will track the target vehicle and control the speed of the ACC vehicle so that the ACC vehicle will follow the target vehicle at a safe distance. When the target vehicle moves out of the path or lane of the ACC vehicle, the ACC system ceases tracking the preceding vehicle and returns the ACC vehicle to the value set by the ACC vehicle operator.
ACC systems generally include sensors, a target identification system, a control system, and a mechanism for controlling the ACC vehicle""s speed. In general, the sensors obtain information regarding the speed and position (including the location and bearing)_of the ACC vehicle and the speed and relative position (including the location and azimuth angle relative to the ACC vehicle) of any preceding vehicles. This information is used by the target identification system to determine which, if any, of the preceding vehicles are target vehicles. The information is also used by the control system to control the speed of the ACC vehicle by sending the appropriate signals to the mechanism for controlling the ACC vehicle""s speed.
The sensors include a sensor for sensing the relative speed, location and azimuth angle of the preceding vehicle (the xe2x80x9cpreceding vehicle sensorxe2x80x9d) and sensors for sensing the speed, location and bearing of the ACC vehicle (the xe2x80x9cACC vehicle sensorsxe2x80x9d). The preceding vehicle sensor generally includes a radar source and detector. Alternatively, the preceding vehicle sensor may include any other electromagnetic (including millimeter wave and laser) and sound sources and/or detectors. The preceding vehicle sensor can obtain the location, and azimuth angle of the preceding vehicle relative to the ACC vehicle (the xe2x80x9crelative positionxe2x80x9d) and the speed of the preceding vehicle. The ACC vehicle sensors generally include a speedometer to measure the speed of the ACC vehicle and a yaw rate sensor or a steering wheel sensor to determine the location and bearing (the xe2x80x9cpositionxe2x80x9d) of the ACC vehicle and/or the curvature of the ACC vehicle""s present path from the angular velocity of the ACC vehicle.
The target identification system determines which of the preceding vehicles is a target vehicle. Additionally, the target identification system may distinguish preceding vehicles from road-side objects. The target identification system may determine which of the preceding vehicles is a target vehicle by determining which of the preceding vehicles is in the same lane as or is in the path of the ACC vehicle. Once a preceding vehicle is identified as a target vehicle, its position is monitored (xe2x80x9ctrackedxe2x80x9d) as a target by the target vehicle sensor and its location and azimuth angle are used by the ACC control.
The control system generally includes a system that controls the ACC vehicle""s speed on the basis of the position of the target vehicle relative to the ACC vehicle obtained by the preceding vehicle sensor and the speed and position of the ACC vehicle obtained from the ACC vehicle sensors. The mechanism for controlling the ACC vehicle""s speed is generally a throttle control and/or a brake control which is generally controlled by the control system.
However, these known ACC systems are not typically able to accurately identify a target vehicle in certain situations. For example, FIGS. 1A-1F illustrate the some of the various positional situations that exist for an ACC vehicle and a preceding vehicle traveling on the same road. FIGS. 1A-1E illustratrate an ACC vehicle 30 following a target vehicle 40 around a curve 54 in a road 50 while FIG. 1F illustrates an ACC vehicle 30 following a target vehicle 40 on a road 80. More specifically, FIG. 1A illustrates the positional situation where both the ACC and target vehicles 30 and 40, respectively, have not yet entered the curve 54 and are in location 52 on road 50. FIG. 1B illustrates the positional situation where the ACC vehicle 30 has not yet entered the curve 54 and is in location 52 and the target vehicle 40 is in the curve 54. FIG. 1C illustrates the positional situation where both the ACC and target vehicles 30 and 40, respectively, are in the curve 54. FIG. 1D illustrates the positional situation where the ACC vehicle 30 is still in the curve 54 and the target vehicle 40 has left the curve 54 and is in location 56. FIG. 1E illustrates the positional situation where both the ACC and target vehicles 30 and 40, respectively, have left the curve and are in location 56. FIG. 1F illustrates a positional situation on a road 80 where both the ACC vehicle 30 and the target vehicle 40 are on a curve in the road 80 wherein the curvature or radius of the curve is not constant. For the positional situations shown in FIGS. 1A, 1C and 1D (the xe2x80x9cnon-transient situationsxe2x80x9d or xe2x80x9cuniform situationsxe2x80x9d), known methods can reasonably determine whether the preceding vehicle is in the same lane as the ACC vehicle. However, these known methods encounter problems when attempting to determine whether the preceding vehicle is in the path of the ACC vehicle when the preceding and ACC vehicles are in the positional situations shown in FIGS. 1B, 1D and 1F (the xe2x80x9ctransient situationsxe2x80x9d or xe2x80x9cnon-uniform situationxe2x80x9d).
Known ACC systems have difficulty tracking target vehicles around curves in the road, namely in the xe2x80x9cnon-uniform situation.xe2x80x9d Often in these situations, known ACC systems will completely_stop tracking the target vehicle. Generally, known ACC systems have no effective way of determining whether the preceding vehicle is in the same lane as or in the future path of the ACC vehicle for all positional situations. This problem is particularly acute in the positional situations shown in FIGS. 1B, 1D and 1F.
One known ACC system identifies which preceding vehicles are target vehicles by using the theoretical relationship between the azimuth angle and relative velocity between the ACC vehicle and the preceding vehicle as defined in a phase chart (see U.S. patent application Ser. No. 09/815187. This known ACC system works well for identifying a preceding vehicle as a target vehicle in the xe2x80x9cnon-uniform situationxe2x80x9d because it can determine whether the preceding vehicle is in the path of the ACC vehicle. However, this known system cannot be applied to uniform situations for several reasons. One reason is that the relationship between the azimuth angle and relative velocity is determined empirically and therefore requires that a great deal of experimental data be collected and stored in the system. Another reason is that and the system requires many complex calculations.
It is an object to provide a method and apparatus that can identify whether a preceding vehicle is a target vehicle and if a target vehicle is in the same lane as an ACC vehicle in both the uniform and non-uniform situations without the disadvantages of the known systems. It is also an object to provide a method and apparatus for determining the radius of a curve in the road from the position trace of a preceding vehicle. It is also an object to provide a method and self-contained apparatus for determining whether a preceding vehicle is a target vehicle and if a target vehicle is in the same lane as the ACC vehicle by using the position trace of the target vehicle. It is also an object to provide an ACC system that can accurately control the speed of the ACC vehicle in all non-uniform situations as well as in uniform situations without the need for empirical data. Other objects and advantages of the methods and apparatuses disclosed herein will be apparent from the following summary and detailed description of the preferred embodiments.
An apparatus and method are provided for identifying a preceding vehicle as a target vehicle in both the uniform_and non-uniform situations. The method generally includes, determining a position of an ACC vehicle; estimating a position of the preceding vehicle relative to the position of the ACC vehicle; creating a time-dependent position trace of the preceding vehicle; estimating a radius of the position trace of the preceding vehicle by applying circular curve fitting to the position trace of the preceding vehicle; and determining whether the preceding vehicle is a target vehicle by the degree of the fitting. The system can also determine if a target vehicle is in the same lane as the ACC vehicle by examining the position of the ACC vehicle relative to the estimated position trace of the target vehicle.
An apparatus includes a self-contained target identification system, which generally includes, a memory device that stores the position information for an ACC vehicle and the relative position information for the preceding vehicle; a processor and computer software that computes the relative position of a preceding vehicle using the position information of the ACC vehicle; creates a position trace; and estimates a radius of the position trace by using curve fitting. Curve fitting is accomplished by transforming the position trace into a ("xgr",xcex7) local coordinate system, where the reference point is one of the positions of the preceding vehicle. The target identification system may also be included in a self-contained ACC system or collision avoidance system that also includes, a preceding vehicle sensor; at least one ACC vehicle sensor; and an ACC vehicle throttle control.
Described herein are numerous embodiments which will be understood by those skilled in the art based on the present disclosure. Some of these are described below and are represented in the drawings by means of several figures, in which: